1. Field of the Invention
The present invention generally relates to signal detecting networks and, more particularly, to a passive detection technique based on correlation characteristics of split beam inputs with given angular rates between a detection sensor platform and a target source.
2. Description of the Prior Art
There are two approaches to the problem of detecting a target, such as a submarine, in a noise field, and they are the use of active or passive sonar. The subject invention belongs to the latter category. In general, passive sonar has three methods of detecting a target. These are an energy detector, a cross-correlation detector and a target angle variance detector. An energy detector usually processes power or amplitude level of a received signal. If the level exceeds a predetermined level, then a target is detected. On the other hand, a cross-correlator detector computes the cross-correlation coefficient between two phase offset beams. Since the magnitude of this correlation coefficient is different between the background noise and a target, a threshold can be set for target detection. The target angle variance detector uses the principle that the measurement of the angle variance from a pair of phase offset beams will drop from that for noise alone as soon as a target is present.
All these methods require a detection threshold with a signal-to-noise ratio range from zero to 10 dB which severly limits a target detection range. What is needed is a passive target detection system which is not as severly range limited as existing passive detection systems.